PEIRCE. — BEHAVIOR OF THE CORE OF AN ELECTROMAGNET. Ill 



my own experience shows that it is not always easy to measure all the 

 small areas, especially the lower ones, with the desirable accuracy, 

 when the width (OF) of the whole diagram is only 12 or 14- 

 centimeters. 



If in the U diagram there is only one intermediate stage, and if the 

 core is in a given magnetic condition at the outset, the change in the 

 magnetic flux, due to a current of given final value, ought not to differ 

 by more than perhaps a fraction of one per cent from the correspond- 

 ing change when there is no intermediate step and the case is rep- 

 resented by V. Sometimes a series of U diagrams, each with but one 



Figure 8. 



The areas between the asymptote and the curves Zand P are proportional to 

 the changes of magnetic flux through the circuit caused by direct and reverse 

 currents of the same final strength. 



intermediate step, at a place determined by a proper choice of r, may 

 be made to yield very accurate information about the permeability of 

 the large mass of metal which will suit some special use of the magnet. 

 Figure 8, which resembles in general design some diagrams given by 

 Dr. Thornton, shows a "direct curve" (Z) and a "reverse curve " (P) 

 for a certain magnet. The area OZXY represents the change of 

 magnetic induction when the core covers the arc PFM (Figure 6) on 

 the hysteresis diagram belonging to the journey ; the area OPQXY 

 represents the change of magnetic flux when the core takes the 

 journey corresponding to the arc QUZM on the hysteresis diagram. 

 The doubly shaded area represents the flux change corresponding to 

 theKne QUZMKP. 



